This invention relates to conditioning ink jet orifices.
In ink jet printing, ink is ejected from a narrow orifice in the direction of a substrate. In one type of ink jet printing, known as drop on demand printing, the ink is ejected in a series of droplets. The droplets may be produced and controlled using a piezoelectric ink jet head which has a large number of orifices, each of which is separately controllable to selectively eject ink at desired locations, or pixels, of the image. For example, an ink jet head may have 256 orifices that have a spacing for a printing resolution of 100 pixels (dots) per inch (dpi) or more. This dense array of orifices allows complex, highly accurate images to be produced.
The quality of the images suffers, however, if one or more of the orifices becomes obstructed. For example, a partially obstructed orifice may alter the direction, size, or stability of the droplets. A fully obstructed orifice reduces print quality by causing gaps in the image.
In an aspect, the invention features conditioning an ink jet orifice by illuminating the orifice with radiation. In another aspect, the invention features conditioning an ink jet orifice using a printing station arranged to permit the print head to print an image on a substrate, and a radiation source arranged to illuminate the orifice. In another aspect, the invention features conditioning an ink jet orifice using a testing station arranged to test the operation of the orifice, and a radiation source arranged to illuminate the orifice.
Embodiments may include one or more of the following. The radiation is selected to remove organic contaminant material. The organic material is selected from the group consisting of ink, polymer, and protein. The radiation is selected.to smooth regions of the ink jet head proximate the orifice. The radiation is UV radiation. The radiation is provided by an excimer laser. The excimer laser has a wavelength of about 248 nm and a fluence of about 0.3 to about 1.5 Joule/cm2, e.g., about 0.5 Joule/cm2.
Embodiments may also include one or more of the following. The radiation,is focused to a focal point. The radiation is selected to remove contamination to a depth inside the orifice no greater than about 15 xcexcm. The focal point is inside the orifice. The radiation has a beam diameter smaller than the width of the orifice. The radiation impinges the orifice at an angle with respect to the axis of the orifice. A coolant is used in proximity with the orifice. The coolant is gas. An ozone-forming gas and radiation at a select wave length are used to form ozone.
Embodiments may also include one or more of the following. The orifice is in a plate fabricated from metal, polymer, or ceramic. The orifice has a diameter of about 70 xcexcm or less, e.g., about 15 to about 50 xcexcm. The plate has a plurality of orifices separated by about 0.015 inch or less, e.g., about 0.004 to about 0.012 inch. The ink jet orifice is an ink jet orifice for a piezoelectric drop on demand ink jet head.
Embodiments may include one or more of the following. The operation of the orifice is tested by jetting a test image. The image is visually inspected or electronically inspected. A transport arrangement transports the orifice between a printing station to an illuminating station including the source of radiation and a testing station. The transport arrangement includes a rail system.
Embodiments may include one or more of the following advantages. For example, print head orifices can be quickly, efficiently, and inexpensively cleared of obstructions, such as those arising during manufacture or use. The conditioning can greatly improve the manufacturing yield of print heads. For example, print heads rejected for droplet instability or orifice obstructions may be recovered by radiation conditioning. Heads that develop obstructions in use, e.g., dried ink obstructions, can be quickly and easily conditioned without the need to replace the head or orifice plate. Print heads can also be conditioned even if they do not have an obstruction, to smooth rough surfaces and sharp corners adjacent to the orifice, which can improve droplet formation and jetting characteristics. Print heads can also be radiation conditioned to remove conformal coatings.
Further advantages, aspects, and features, follow.